1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for jetting ink drops from a nozzle opening by vibration of a piezoelectric-vibrator and printing on a recording paper or others, and a method for driving an ink-jet recording head thereof.
2. Description of the Related Art
Generally, an ink-jet recording apparatus has a recording head with many nozzle openings in the sub-scanning direction (the recording paper feeding direction). The recording head is moved in the main scanning direction (the direction of the recording paper width) by a carriage mechanism. Predetermined paper feeding is executed, and a desired printing result is obtained. On the basis of dot pattern data obtained by expanding print data input from a host computer, ink drops are jetted from each nozzle opening of the recording head respectively in predetermined timing. Each of the ink drops is jetted and adhered to a print recording medium of a recording paper or others, thereby dots are formed and printing is carried out.
The recording head mentioned above generally transfers deformation of a piezoelectric-vibrator to a vibration plate so as to contract a pressure generating chamber, increase the inner pressure, and jet ink drops from the nozzle openings. The aforementioned deformation of the piezoelectric-vibrator is obtained by changing a drive voltage input to the piezoelectric-vibrator. Therefore, ink drops are jetted by expanding and contracting the pressure generating chamber.
Each piezoelectric-vibrator used for the recording head of the ink-jet recording apparatus is assumed as an ideal capacitor from the viewpoint of design. Namely, the voltage (segment voltage) of the piezoelectric-vibrator is considered to continuously hold the voltage during the time of non-supply of the drive signal mentioned above. On the basis of this consideration, the drive signal is preset so as to keep the initial voltage and terminal voltage on the same level.
However, an actual piezoelectric-vibrator has an insulation resistance. Therefore, when it is left as it is with no drive signal supplied, it is found that the vibrator voltage gradually drops by natural discharge. The drop of the vibrator voltage, for example, is caused by non-uniformity of the piezo-electric body of the piezo-electric layer. Moreover, when the electrodes of the piezoelectric vibrator are short-circuited by a foreign substance existing between the electrodes, the drop of the vibrator voltage is caused.
Accordingly, a means for applying a voltage to the piezoelectric vibrator in the standby state with no drive signal applied (hereinafter referred to as a voltage recovery means) is proposed so as to recover the vibrator voltage dropped by discharge up to the intermediate voltage which is the standby voltage of the piezoelectric vibrator. For example, in Japanese Patent No. 3097155 (Japanese Patent Laid-Open Publication No. 4-310748, Japanese Patent Application No. 3-77718), a piezoelectric element charging means for compensating for a reduction in the charge due to discharge of the piezo-electric element by applying the charging voltage to the piezo-electric element in different timing from the print timing of the piezo-electric element is described.
Meanwhile, the drop amount of the vibrator voltage increases as the time from supply end of an earlier drive signal to supply start of a later drive signal, that is, the non-supply period of the drive signal becomes longer. Further, when the film thickness of the piezoelectric vibrator becomes thinner (as the electric field intensity becomes higher), the vibrator voltage drops remarkably. As a result, in a piezoelectric vibrator of a small volume (thin film thickness) requested recently, even if the non-supply period of the drive signal is very short, the difference between the vibrator voltage dropped due to discharge and the initial voltage of the later waveform element increases.
Furthermore, recently, to increase the height difference of the vibration damping waveform to be applied to the piezoelectric vibrator after ink drops are jetted, there is a tendency to set the intermediate voltage, which is the standby voltage, high. The drop amount of the vibrator voltage increases as the vibrator voltage increases. Therefore, as the intermediate voltage is set higher, the drop amount of the vibrator voltage increases.
As mentioned above, recently, the drop amount of the vibration voltage tends to increase. When the vibrator voltage is recovered by the voltage recovery means in a state that the vibrator voltage drops greatly, a problem arises that ink drops are accidentally jetted from the nozzle opening at the same time.
In the conventional ink-jet recording apparatus mentioned above, it is very difficult to include both the drive waveform for medium dots and the drive waveform of minute dots in the drive signal (COM) in one print cycle (one drive cycle). The reason is that the standby voltage suited to the drive waveform for medium dots and the standby voltage suited to the drive waveform for minute dots do not coincide with each other generally. When the standby voltage suited to the drive waveform for medium dots is fit to the standby voltage suited to the drive waveform for minute dots, the height difference of the drive waveform for medium dots itself becomes too large. As a result, a problem arises that at the time of jet of medium dots, air bubbles are apt to be taken into the nozzle opening. When air bubbles are taken into the nozzle opening like this, the inner pressure of the pressure generating chamber is not increased normally. As result, ink drops are not jetted normally, causing defective jet.
In the conventional ink-jet recording apparatus mentioned above, even if the ink viscosity is changed due to changing of the environmental temperature around the recording apparatus, ink drops are jetted by the same drive signal regardless of changing of the environment. Therefore, for example, when the ink viscosity is lowered due to a high-temperature environment or others, the meniscus is apt to become unstable and air bubbles are easily taken into the nozzle opening as mentioned above. Furthermore, when the operation environment of the recording apparatus is changed and the ink viscosity is changed, the jet characteristics are also changed and a problem arises that a fixed print quality cannot be easily obtained.
The present invention was developed with the foregoing in view and is intended to provide an ink-jet recording apparatus and a method for driving an ink-jet recording head thereof for surely preventing accidental ink drops at the time of recovery of the vibrator voltage by the voltage recovery means.
Another object of the present invention is to provide an ink-jet recording apparatus and a method for driving an inkjet recording head thereof for jetting ink drops without taking air bubbles into the nozzle opening.
Still another object of the present invention is to provide an ink-jet recording apparatus and a method for driving an ink-jet recording head thereof for preventing air bubbles from taking into the nozzle opening even if the environmental conditions around the recorder are changed.
According to the present invention, an ink-jet recording apparatus includes: a recording head having a piezoelectric vibrator for expanding and contracting a pressure generating chamber connected to a nozzle opening; and drive signal generator for generating a drive signal to be applied to said piezoelectric vibrator so as to drive said piezoelectric vibrator; wherein said drive signal includes an expansion waveform element for changing a voltage so as to expand said pressure generating chamber, a contraction waveform element for changing a voltage so as to contract said pressure generating chamber expanded by said expansion waveform element and jet an ink drop from said nozzle opening, and a vibration damping waveform element which changes from a terminal voltage of said contraction waveform element to a vibration damping voltage so as to expand said pressure generating chamber contracted by said contraction waveform element in order to suppress a residual vibration of a meniscus of said pressure generating chamber after jetting said ink drop, wherein an initial voltage and a terminal voltage of said drive signal are equal to each other and equivalent to a standby voltage which is set as a voltage of said piezoelectric vibrator at a time of non-supply of said drive signal, and wherein said vibration damping voltage lies between said standby voltage and a maximum voltage of said drive signal.
Preferably, said expansion waveform element includes a front part of waveform element, a back part of waveform element positioned behind said front part of waveform element, and a waveform element connection for connecting a terminal end of said front part of waveform element and a starting end of said back part of waveform element, wherein said waveform element connection is positioned at an intermediate voltage between said standby voltage and said maximum voltage, and wherein an inclination of said front part of waveform element is smaller than an inclination of said back part of waveform element.
Preferably, a difference between said standby voltage and said intermediate voltage is reduced in accordance with rising of an environmental temperature.
Preferably, a continuation time of said front part of waveform element is set longer than an intrinsic vibration cycle of said pressure generating chamber.
Preferably, said drive signal includes a return waveform element which is positioned behind said vibration damping waveform element and changes from said vibration damping voltage to said standby voltage.
Preferably, an inclination of said return waveform element is smaller than an inclination of said contraction waveform element.
Preferably, a continuation time of said return waveform element is set longer than said intrinsic vibration cycle of said pressure generating chamber.
Preferably, said standby voltage is a minimum voltage of said drive signal.
Preferably, a continuation time of said back part of waveform element is set longer than an intrinsic vibration cycle of said piezoelectric vibrator and shorter than said intrinsic vibration cycle of said pressure generating chamber.
Preferably, a continuation time of said contraction waveform element is set longer than an intrinsic vibration cycle of said piezoelectric vibrator.
Preferably, a continuation time of said vibration damping waveform element is set longer than an intrinsic vibration cycle of said piezoelectric vibrator.
Preferably, a contraction holding waveform element for holding a contraction condition of said pressure generating chamber contracted by said contraction waveform element succeeds said contraction waveform element and a total continuation time of said contraction waveform element and said contraction holding waveform element is set so as to be made practically equal to integer times of said intrinsic vibration cycle of said pressure generating chamber.
Preferably, said total continuation time of said contraction waveform element and said contraction holding waveform element is set so as to be made practically equal to said intrinsic vibration cycle of said pressure generating chamber.
Preferably, a voltage difference of said contraction waveform element itself is reduced in accordance with rising of an environmental temperature.
Preferably, a voltage difference of said vibration damping waveform element itself is increased in accordance with rising of an environmental temperature.
Preferably, an expansion holding waveform element for holding an expansion condition of said pressure generating chamber expanded by said expansion waveform element succeeds said expansion waveform element, and wherein a continuation time of said expansion holding waveform element is increased in accordance with rising of said environmental temperature.
According to the present invention, a method for driving an ink-jet recording head having a piezoelectric vibrator for expanding and contracting a pressure generating chamber connected to a nozzle opening, includes: a step of generating a drive signal to be applied to said piezoelectric vibrator so as to drive said piezoelectric vibrator; and a step of applying said drive signal to said piezoelectric vibrator and driving said piezoelectric vibrator; wherein said drive signal includes an expansion waveform element for changing a voltage so as to expand said pressure generating chamber, a contraction waveform element for changing a voltage so as to contract said pressure generating chamber expanded by said expansion waveform element and jet an ink drop from said nozzle opening, and a vibration damping waveform element for changing a voltage from a terminal voltage of said contraction waveform element to a vibration damping voltage so as to expand said pressure generating chamber contracted by said contraction waveform element in order to suppress a residual vibration of a meniscus of said pressure generating chamber after jetting said ink drop, wherein an initial voltage and a terminal voltage of said drive signal are equal to each other and equivalent to a standby voltage set as a voltage of said piezoelectric vibrator at a time of non-supply of said drive signal, and wherein said vibration damping voltage lies between said standby voltage and a maximum voltage of said drive signal.
Preferably, said expansion waveform element includes a front part of waveform element, a back part of waveform element positioned behind said front part of waveform element, and a waveform element connection for connecting a terminal end of said front part of waveform element and a starting end of said back part of waveform element, wherein said waveform element connection is positioned at an intermediate voltage between said standby voltage and said maximum voltage, and wherein an inclination of said front part of waveform element is smaller than an inclination of said back part of waveform element.
Preferably, a difference between said standby voltage and said intermediate voltage is reduced in accordance with rising of an environmental temperature.
Preferably, a continuation time of said front part of waveform element is set longer than an intrinsic vibration cycle of said pressure generating chamber.
Preferably, said drive signal includes a return waveform element which is positioned behind said vibration damping waveform element and changes from said vibration damping voltage to said standby voltage.
Preferably, an inclination of said return waveform element is smaller than an inclination of said contraction waveform element.
Preferably, a continuation time of said return waveform element is set longer than said intrinsic vibration cycle of said pressure generating chamber.
Preferably, said standby voltage is a minimum voltage of said drive signal.
Preferably, a continuation time of said back part of waveform element is set longer than an intrinsic vibration cycle of said piezoelectric vibrator and shorter than said intrinsic vibration cycle of said pressure generating chamber.
Preferably, a continuation time of said contraction waveform element is set longer than said intrinsic vibration cycle of said piezoelectric vibrator.
Preferably, a continuation time of said vibration damping waveform element is set longer than said intrinsic vibration cycle of said piezoelectric vibrator.
Preferably, a contraction holding waveform element for holding a contraction condition of said pressure generating chamber contracted by said contraction waveform element succeeds said contraction waveform element, and wherein a total continuation time of said contraction waveform element and said contraction holding waveform element is set so as to be made practically equal to integer times of said intrinsic vibration cycle of said pressure generating chamber.
Preferably, said total continuation time of said contraction waveform element and said contraction holding waveform element is set so as to be made practically equal to said intrinsic vibration cycle of said pressure generating chamber.
Preferably, a voltage difference of said contraction waveform element itself is reduced in accordance with rising of an environmental temperature.
Preferably, a voltage difference of said vibration damping waveform element itself is increased in accordance with rising of an environmental temperature.
Preferably, an expansion holding waveform element for holding an expansion condition of said pressure generating chamber expanded by said expansion waveform element succeeds said expansion waveform element, and wherein a continuation time of said expansion holding waveform element is increased in accordance with rising of an environmental temperature.